Half-Life 2
Run in high-quality mode but without additional image enhancement, all cards are pretty damn quick. Half-Life 2, though, is a game that relies on the CPU and subsystem's performance far more than other games, so the lack of impact from a 512MB framebuffer is expected.
There's a consistent, ever-so-slight performance improvement at the highest setting, although that's probably more down to a slightly faster Ultra core than anything else. Take a look at the performance increase for Radeon X800 XL 256MB and 512MB cards. That's not mirrored for GeForce 6800 Ultra cards. What's worrying, from a performance point of view at least, is that a cheaper GeForce 7800 GTX is around 50% faster. Still, a ~65FPS average is more than acceptable.
